A function to get the week number and a tester function for it.

test_utils.py

import calendar
import datetime
from math import ceil


def get_week_number(date: datetime.date) -> int:
    """
    Credits goes to:https://stackoverflow.com/a/66176965/9309611
    """
    return (date.day - 1 + (date.weekday() - date.day + 1) % 7) // 7 + 1


def test_get_week_number():
    for year in range(datetime.date.min.year, datetime.date.max.year + 1):
        for month in range(1, 12 + 1):
            month_days = calendar.monthcalendar(year, month)

            for week_number in range(1, len(month_days) + 1):
                for weekday in range(7):
                    day = month_days[week_number - 1][weekday]
                    if day == 0:
                        continue
                    date = datetime.date(year, month, day)

                    assert week_number == get_week_number(date), \
                        f'{date} week from calendar: {week_number},' \
                        f' from function: {get_week_number(date)}'